1. Field of the Invention
The present invention relates to two-cycle engine oil compositions and to ester base stocks which are components thereof. The compositions of the invention require no miscibility-enhancing solvents and are readily biodegradable.
2. Description of the Related Art
The two-cycle (two stroke) engine has gained considerable popularity as a power source for such devices as outboard motors, snow mobiles, mopeds and a variety of landscaping equipment, e.g., lawnmowers, chain saws, string trimmers and blowers. The widespread use of two-cycle engines is due primarily to their simple design and lightweight construction, their ability to provide high power output with quick starts at low temperature and their relatively low cost.
Two-cycle engines are operated using a mixture of gasoline and a lubricant in prescribed proportions. The lubricant must provide satisfactory performance characteristics under severe operating conditions. Lubricants for two-cycle engines ar generally composed of a mineral oil or synthetic base fluid, performance additives and a solvent, ordinarily a relatively low boiling petroleum distillate, to enhance gasoline/lubricant miscibility.
The technologies developed to date for reducing exhaust emissions from four-cycle car and truck engines have not been successfully adapted to two-cycle engines. Hence, there is growing public concern over the high levels of hydrocarbon emissions from these small engines, as hydrocarbons do not readily biodegrade.
The hydrocarbon emissions are a consequence of the basic design of the engine. Specifically, in the power stroke of a typical two-cycle engine, air, oil and fuel are drawn into the crank case as the combined charge is compressed in the space above the piston. In the exhaust stroke, the burnt gases are discharged through exhaust ports, and a fresh combustible charge is transferred from the crank case to the space above the piston. Because the exhaust ports open before and close after transfer of the fresh combustible charge occurs, as much as 20% of the fresh charge will be discharged unburnt with the exhaust. Consequently, hydrocarbon emissions far exceed the level of emissions from a comparable four-cycle engine.
Water-cooled outboard motors exhaust directly into the water, giving rise to water pollution, whereas the other devices mentioned above, which are equipped with air-cooled two-cycle engines, produce emissions that pose a serious air pollution problem. For example, the California Air Research Board has determined that many two-cycle engines produce up to fifty times the pollution of truck engines per horsepower hour.
The above-noted pollution problems are exacerbated by the presence of volatile organic solvents in the lubricant. Moreover, some of the solvents used as miscibility enhancers, such as Stoddard solvent, have relatively low flash points, thus creating a potential fire risk, which is of particular concern in connection with the storage and transportation of such products.
Thus, a need exists for a two-cycle engine oil composition which is formulated so as to prevent pollution by protecting against emission of harmful hydrocarbons into the environment, and to reduce the hazard potential of the solvent-containing lubricants, especially in storage and in transit. These objectives must be obtained, however, while simultaneously satisfying stringent performance standards, e.g., good lubricity and detergency, particularly on piston rings, superior anti-seizure properties and high gel/floc resistance, and providing optimum miscibility of lubricant and fuel over the applicable range of operating conditions.
In accordance with the present invention, there is provided a biodegradable ester base stock and a two-cycle engine oil composition containing same which is adapted for use in both water-cooled and air-cooled two-cycle engines. The oil composition of the invention is formulated so as to eliminate the need for a conventional solvent, thereby substantially reducing not only the pollution potential of two-cycle engines lubricated therewith, but the hazard risk inherent in solvent-containing formulations.
According to one embodiment of the present invention, there is provided an ester base stock for a two-cycle engine oil composition, which consists essentially of a blend of (a) a first polyol ester comprising, as its reactive components, a neopentylpolyol and a C16-C20 branched chain, saturated monocarboxylic acid, and (b) a second polyol ester comprising, as its reactive components, a neopentyl polyol and a carboxylic acid selected from the group consisting of at least one C5-C10 linear, saturated monocarboxylic acid, or at least one C16-C20 linear or branched chain, unsaturated monocarboxylic acid.
According to another embodiment of this invention, there is provided an ester base stock for a two-cycle engine oil composition, which consists essentially of a blend of (a) a first polyol ester comprising, as its reactive components, a neopentyl polyol and a C8-C10 linear, saturated monocarboxylic acid and (b) a second complex polyol ester comprising, as its reactive components, a neopentyl polyol, a C6-C12 dicarboxylic acid and a C5-C10 linear or branched chain, saturated monocarboxylic acid.
A solvent substitute, if desired, may optionally be incorporated in the ester base stocks of the invention. Suitable for this purpose are any of various relatively low molecular weight esters comprising as the reactive components thereof, a C8-C13 linear or branched chain monohydric alcohol and a C5-C12 linear or branched chain carboxylic acid.
The ester base stocks of the invention are characterized by their superior biodegradability, flash point and viscosity properties, as compared with two-cycle engine lubricant base stocks heretofore available. The biodegradability of the ester base stocks of the invention is greater than 80%, as determined by CEC-L-33-T-82. Each of the ester base stocks of the invention has a flash point of at least 175xc2x0 C. The kinematic viscosity of the ester base stocks of the invention is less than 15 cSt at 100xc2x0 C.
The two-cycle engine oil compositions of the invention are composed of the above-described base stocks and any of the performance additive packages known in the art, preferably ashless detergent/dispersant additives, e.g., reaction products of polyamines and relatively long chain fatty acids. In addition to having the desirable biodegradability, flash point and viscosity properties noted above, the two-cycle engine oil compositions of the invention have excellent miscibility with gasoline, in fuel/oil ratios between 16:1 to 100:1